1. Field of the Invention
The present invention relates to acryloyloxypropylalkoxysilane compositions, to a process for their preparation, and to the use thereof in silicon-containing coating materials and paints.
2. Discussion of the Background
Acryloyloxypropylalkoxysilanes, such as 3-methacryloyloxypropyltrimethoxysilane are important starting materials for the production of silicon-containing coating materials and paints (EP-B 0 324 747 and EP-B 0 267 698). Frequently, the pH of these silanes plays a decisive role in the production and formulation of coating materials and paints and affects the storage properties of the coating materials and paints. Within the industry there is a requirement for acryloyloxypropylalkoxysilanes having a pH of from about 5 to 6.
However, conventional acryloyloxypropylalkoxysilanes, prepared by various processes (see U.S. Pat. Nos. 3,258,477, 4,946,977, 5,117,027), have intrinsic pH values which are only from around 3 to &lt; 5.
Organosilanes are not protonic or Lewis acids in the conventional sense, but in contact with water they cause an acidification of the aqueous phase. The degree of acidification can be determined by measuring the pH by known methods. By definition, the pH measured in water is assigned to the organosilane.
While an increase in the pH of acryloyloxypropylalkoxysilanes by addition of basifying compounds such as alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal alcoholates or alkaline earth metal alcoholates is indeed possible, such mixtures are not stable on storage, and the acrylic ester bond is rapidly cleaved after a short time (G. Rossmy and G. Korner, Makromolekulare Chem. 73 (1964), p. 85-108). The cleavage occurs with particular readiness in the presence of proton-donating solvents such as alcohols or water.